We are continuing this project, which began in 1993. We have been working to establish culture and enrichment procedures for human megakaryocytes. Until 8/95, we were working with collections of peripheral blood from normal volunteers. We have now had a protocol approved by the NHLBI IRB for the collection of bone marrow specimens from normal volunteers, which we expect to be richer in megakaryocyte progenitors. Once we have established sufficient enrichment in cultures derived from normal individuals, we will begin collecting samples of bone marrow and peripheral blood from patients with clonal hematologic disorders. We will compare messages from both sources by a variety of techniques.